Numerical study of vortical flows shedding from a bluff body with a wavy trailing edge

Abstract

Previous experimental studies have shown that applying a geometric sinusoidal disturbance to the trailing edge of a quasi-streamlined bluff body can result in substantial base pressure recovery when compared against a normal straight edged configuration. Here, a numerical simulation at a Reynolds number of 2500 is used to examine in detail various aspects of the flow such as the base pressure distribution, vortex shedding mechanism and frequency selection in relation to a variation in the wavelength of the sinusoidal disturbance. The concentration of dye released along the upper trailing edge of the body is tracked by solving the scalar transport equation to facilitate visualization and comparison of the flow field analogous to the dye precipitation technique used in previous studies. The results show that a sinusoidally shaped trailing edge with fixed amplitude and a wavelength which is 5 times the base height displays a reduction of more than 36% in the mean drag coefficient when compared to the straight edged case. This reduction is traced to a lengthening of the mean recirculation region, a marked drop in the velocity fluctuation at the dominant frequency of the wake and a reduction in the spanwise component of the wake vorticity. Conversely, this reduction in the drag coefficient is substantially diminished for a sinusoidal trailing edge with a longer wavelength. For such a configuration, the flow is characterized by the formation of vortex dislocations which causes the flow to have a less regular character. Finally, a shorter wavelength of four base heights results in a reduction of the mean recirculation region with an attendant increase in the spanwise vorticity. This leads to a drag coefficient similar to that of the straight trailing edge.